Mathematical squaring device of the electron tube type



Oct. 7, 1947. M. T. BAGLEY MATHEMATICAL SQUARING DEVICE OF THE ELECTRONTUBE TYPE Filed Aug. 11, 1944 -':III

INVENTOR W. a ATTORN E Patented Oct. 7, 1947 UNITED STATES PATENT OFFICEMATHEMATICAL SQUARING DEVICE OF THE ELECTRON TUBE TYPE.

Application August 11, 1944, Serial No. 549,112

4 Claims. 1

This invention relates to systems for deriving an algebraic squarefunction of another function, and in particular to such devices asemploy electron tubes for that purpose.

A principal object of the invention is to provide a novel and morestable squaring function device using electron tubes.

Heretofore in electronic devices for producing a squared output functionfrom a given input control function, it hasbeen customary .to use a pairof grid-controlled tubes connected in balanced phase opposition to theinput circuit, of which the well-known push-pull arrangement is typical.ne of the disadvantages of such prior arrangements is that in order toderive the necessary squared output function, it is necessary to selectthe grid controlled push-pull tubes with substantially identicalcharacteristics. This is particularly bothersome because the tubes musthave substantially identical plate current-grid voltage characteristicsin the curved portions thereof. Furthermore, even if a pair of perfectlymatched tubes is initially selected, after continued use one tube maychange slightly with respect to the other. This limitation is thereforepeculiar to grid-controlled tubes. I have found that the necessarysquared function can be achieved wlthout'using matched grid-controlledtubes. Accordingly, another principal object of the invention relates toa squaring system having the desirable advantages of push-pullgridcontrolled tubes, but using a pair of-diodes so connected to asingle grid-controlled tube that substantially only the even harmonicsof an input signal appear in the output of the grid-controlled tube.

Another principal object is to provide a novel phase inversion circuitemploying a single g idcontrolled tube and a pair of diodes.

A feature of the invention relates to a circuit arrangement wherein asingle grid-controlled tube is operated on the non-linear portion of itscontrol grid voltage vs. plate current characteristic, and a squaringaction is obtained in the output by using a special double diodecontrolled input to suppress odd harmonics in the output.

Another feature relates to a novel network for producing a squaredoutput function of an input control signal, including not only the A. C.components of the said signal but also D. C. components thereof.

A further feature relates to a novel phase inverter which operatessatisfactorily on pure A. C. input signals or on signals having both A.C. and D. C. components.

A still further feature relates to the novel organization, arrangementand relative interconnection of parts which cooperate to produce animproved algebraic squaring device.

Other features and advantages not specifically enumerated will becomeapparent after consider- ,ing the following detailed descriptions andthe appended claims.

While the invention finds its immediate utility in so-called automaticcalibrators where an algebraic square function is to be derived from aninput control function, it will be clear that the invention in itsvarious phases is equally well applicable to other uses, particularlythose where even harmonics of input signals are required, and wherephase inversion of both A. C. and D. C. components is required.Therefore in the drawing two preferred embodiments are shown forexplanatory purposes but not by way of limitation thereto.

Fig. 1 is a schematic wiring diagram of a square function derivativesystem for A. C. input signals.

Fig. 2 is a schematic wiring diagram of a square function derivativesystem useful with input signals having both A. C. and D. C. components.

Fig. 3 is a characteristic curve showing the range of operation of thegrid-controlled tube used with the invention.

Referring to Fig. 1, the terminals l, 2 are connectable to any source ofcontrol signals the fundamental voltage of which may represent, for

example, a mathematical function whose square is to be derived at theoutput terminals 3, 4. In order to achieve this squaring function, it isrequisite that the grid-controlled tube 5 be operated on the curvedportion of its EgI characteristic, which should preferably be such thatthe relation between control grid voltage and plate current follows asquare law as represented for example by the section AB of thecharacteristic curve of Fig. 3. It is also requisite that only the evenharmonics, and predominantly the second harmonic, of the input signalwave appear in the output. In order to accomplish the first of these tworequisites, tube 5 has its control grid 6 normally negatively biassed,as for example by bias battery 1, to substantially plate currentcut-off, e. g. at the point A (Fig. 3). In order to achieve the secondof the above requisites, it is necessary to modulate or drive the gridbias 6 by means of a phase inverting circuit. For this purpose the inputsignal is applied through a phase inverting transformer 8 the secondaryof which is connected in opposed balanced relation to the respectiveanodes 9, ill of two rectifier diodes l5, Hi, the cathodes II and I2 ofwhich are connected in common to load resistor I3 and thence to theelectric mid-point H of the secondary winding of transformer 8. Ifdesired, the connection of resistor [3 to the secondary winding may bead- Justable. It will be understood that instead of using two separatediode tubes, the diodes may be in a single envelope constituting anywellknown double diode tube. Likewise while the tube 5 is shown as asimple triode, it will be understood that any other equivalentgrid-controlled tube having two or more grids such for example as ashield grid tube, a pentode tube, or the like, may be employed so longas the characteristic curve of the tube has the necessary square lawfunction near the plate cut-off region as represented in Fig. 3.

It will be observed that the rectified voltages developed across loadresistor l3 are injected into the grid circuit of tube 5 in series withthe bias battery grid 1. However the voltage so developed is of oppositepolarity to the battery I, thus causing the grid 6 to be subjected topotential swings towards the positive direction as represented by therange A-B (Fig. 3).

Because of the full wave rectifying action of diodes 15,16, th voltagedeveloped across resistor i3 is a rectified version of the input controlsignal at terminals I, 2, and is applied to control grid 6. The outputof tube 5 is taken ofi by means of a suitable load resistor 11 atterminals 3. 4, it being understood that the positive D. C. operatingplate potential for tube 5 is represented schematically by battery l8.

With the arrangement described, since the tube 5 is operating on anon-linear portion of its plate current vs. grid voltage characteristiccurve, then the output at terminals 3, 4 will contain only evenharmonics of the input at terminals l, 2, and for positive swings ofgrid 6 the output will be predominantly proportioned to the algebraicsquare of the input signals.

Referring to Fig. 2 there is shown a modification which operates on theD. C. components of the input signal as well as on the A. C. components.In this embodiment the parts which correspond functionally to similarparts in Fig. 1 bear the same designation numerals primed. Howeverinstead of using a transformer coupled phase inverter, a grid-controlledelectron tube 20 is provided, the input terminals l' and 2' beingconnected in D. C. conductive relation across the control grid 2| and inseries with the negative grid bias battery 22 and the cathode loadresistor 23. The series arrangement of the plate-to-cathode space oftube 20 and resistor 23 is shunted by a plate load resistor 24 which isvariably tapped by contact 25 to the anode 9' of rectifier diode 15'.The potential of point Q is therefore a function of the phase of theplate current of tube 20. Likewise the anode H) of rectifier diode I6,is adjustably connected by tap 26 to resistor 21. The positive D. C.operating plate potential for tube 20 is applied through a resistor 28.With this arrangement and with suitable values for resistors 23 and 28the change in potential of points P and Q can be made proportionate tothe signal potential applied at terminals I, 2'. Furthermore as the grid2| swings in a positive direction the potential of point P swingspositive and the potential of point Q swings negatively. On the otherhand for negative swings on grid 2| point P swings ne atively and pointQ swings positively. Thus 4 phase inversion at the anode 9' and I0 isthe same as that of Fig. 1.

By a suitable adjustment of taps 25 and 26 and with no A. C. signalcomponents at terminals i, 2', it is possible to make the.D. C.components of potential at points P and Q equal. Thus changes in phaseof both the A. C. and D. C. components of the input signals results inthe proper phase inversion at points P and Q. The rectified output ofdiodes l5, I6 is taken oif across resistor l3 which controls thepotential of grid 6' in the same way as above described in connectionwith Fig. 1. Ordinarily the resistors 13' and 29 are chosen so that withno signal applied to terminals I, 2', the potential of the common pointS is the same as that of points P and Q, thus maintaining both diodesunbiassed. By means of negative bias battery I the grid 6 is normally(i. e. in the absence of signals at I, 2') substantially at platecurrent cut-off. When signals are applied to I, 2' the potentials at 3'.4' are substantially only the even harmonics of the input signal andhave a squared function with respect to the said input signals.

In both of the foregoing embodiments the diodes I5, 16, and l5, iii, ifnot identical in electrical characteristics can be easily madesufficiently identical for the desired purpose by making the loadresistor l3 or l3 high compared to the plate resistance of the diodesthemselves, as it practically always is. It will be understood of coursethat the signal at the output terminals 3, 4, or 3', 4', consistspredominantly of the second harmonic of the input signal. If a simplesquare function is desired the remaining even harmonics if any arepresent, can be suppressed by suitable suppression or filter networks.It will be understood of course that the invention is not limited to asimple square function, thus if a fourth power function is desired theterminals 3, 4, or 3', -4, may be connected to suitable filter networksof the band pass type for passing only the fourth harmonic. It will alsobe understood that this filter network may be adjustable so as to selectany even harmonic function in the output signal.

Various changes and modifications may be made in the disclosedembodiments without detparting from the spirit and scope of theinvenion.

What is claimed is:

1. In a device of the character described, input terminals, outputterminals, and means to derive at said output terminals a squaredfunction of the signals applied to the input terminals, the lastmentioned means comprising a grid-controlled tube having its inputelectrodes connected to said input terminals, another grid-controlledtube having its output electrodes connected to said output circuit, andmeans to couple the output electrodes of the first tube to the inputelectrodes of the second tube for phase inversion and comprising a pairof rectifier diodes connected respectively to a point in the cathodeload and plate load circuits of said first tube which points aresubstantially of opposite phase for a given input signal, said diodeshaving a common load impedance which is connected in the grid inputcircuit of said second tube.

2. In a device of the character described,-input terminals, outputterminals, a first grid-controlled electron tube having its inputelectrodes connected to said input terminals and including a cathodeload resistor, a second grid-controlled electron tube having its outputelectrodes connected to said output terminals, a plate load resistor forsaid first tube, a pair oi! rectifier diodes, means for adjustablyconnecting the anode of one of said diodes to a point in said plate loadresistor, means for adjustably connecting the anode of the other diodeto a point in the said cathode load resistor, a common load resistor forsaid diodes connected to the cathodes thereof, and means connecting saidcommon load resistor in the grid input circuit of said second tube.

3. A device according to claim 2 in which said second tube has anegative grid bias source connected in series with said common loadresistor in the grid input circuit of said second tube, the voltagesdeveloped across said common load resistor being of opposite polaritywith respect to said bias source.

6 4. A device according to claim 2 in which the cathodes oi the saiddiodes are maintained normaily at the same potential as the anodes inthe absence of signals applied to said input electrodes.

MICHAEL T. BAGLEY.

REFERENCES CITED The following references are of record in the 10 fileoi this patent:

UNITED STATES PATENTS Number Name Date 1,559,992 Schafler Nov. 3, 19252,216,454 Piister Oct. 1, 1940 2,247,468 Barr et al. July 1, 19412,209,395 Fitch July 30, 1940 2,137,545 Schunack Nov. 22, 1938

